I've heard a lot about the GGDT (gas gun design tool), but where can I find it yo use it?

Thanks for the formula, now I have a grasp on this.

What is the best C:B ratio for massive, awesome power on a combustion spud gun? I'm talking super distance and knocking down trees powerful...

Ok, now I agree with losing the double ignitor, it really just gave me an excuse to put more dohickeys on my gun, I'm still lost on the whole barrel length, is there anyway I can figure it out using the ratio without knowing the exact volume, all I know now is the diameter and length of the chamber ...

Ok, I was thinking the two bbq ignitors are side by side with some fitting over the buttons, that when you push the fitting both ignitors spark, would this work?
__
I I

I = bbq ignitor button
__ = fitting over the buttons

I hope that gets my idea across, anyway, I have no way of knowing chamber ...

Hi everyone,
I am new to this site, and have recently become interested in spud guns, so I read most everything on this site, and started to design my first cannon. My question is, I have designed a gun with a 4" diameter chamber, 18" long, and with a 1.5" diameter barrel, using the banjo fittings ...